1. Field of the Invention
The present invention relates to a radiation-curable composition which includes a cyanoacrylate component or a cyanoacrylate-containing formulation, a metallocene component and a polymerizingly effective amount of a photoinitiator to accelerate the rate of cure.
2. Brief Description of Related Technology
Cyancacrylates generally are quick-setting materials which cure to clear, hard glassy resins, useful as sealants, coatings, and particularly adhesives for bonding together a variety of substrates [see e.g., H. V. Coover, D. W. Dreifus and J. T. O""Conner, xe2x80x9cCyanoacrylate Adhesivesxe2x80x9d in Handbook of Adhesives, 27, 463-77, I. Skeist, ed., Van Nostrand Reinhold, N.Y., 3rd ed. (1990)].
Ordinarily, upon contact with substrate materials possessing a surface nucleophile, cyanoacrylate-containing compositions spontaneously polymerize to form a cured material. The cured material exhibits excellent adhesive properties to materials such as metals, plastics, elastomers, fabrics, woods, ceramics and the like. Cyanoacrylate-containing compositions are thus seen as a versatile class of single-component, ambient temperature curing adhesives.
As noted, cyanoacrylate polymerization is typically initiated using a nucleophile. The cyanoacrylate anionic polymerization reaction proceeds until all available cyanoacrylate monomer has been consumed and/or terminated by an acidic species.
Although the predominant mechanism by which cyanoacrylate monomers undergo polymerization is an anionic one, free-radical polymerization is also known to occur in this regard under prolonged exposure to heat or light of an appropriate wavelength. See e.g., Coover et al., supra. Ordinarily, however, free-radical stabilizers, such as quinones or hindered phenols, are included in cyanoacrylate-containing adhesive formulations to extend their shelf life. Thus, the extent of any free-radical polymerization of commercial cyanoacrylate-containing compositions is typically minimal and in fact is especially undesirable for at least the reason stated.
With conventional polymerizable compositions other than those containing cyanoacrylate monomers, radiation cure generally presents certain advantages over other known cure methods. Those advantages include reduced cure time, solvent elimination (which thereby reduces environmental pollution, and conserves raw materials and energy) and inducement of low thermal stressing of substrate material. Also, room temperature radiation cure prevents degradation of certain heat sensitive polymers, which may occur during a thermal cure procedure.
Radiation-curable, resin-based compositions are legion for a variety of uses in diverse industries, such as coatings, printing, electronic, medical and general engineering. Commonly, radiation-curable compositions are used for adhesives, and in such use the resin may ordinarily be chosen from epoxy- or acrylate-based resins.
Well-known examples of radiation-curable, epoxy-based resins include cycloaliphatic and bisphenol-A epoxy resins, epoxidized novolacs and glycidyl polyethers. [See e.g., U.S. Pat. No. 4,690,957 (Fujiokau) and European Patent Publication EP 278 685.] The common cure mechanism for such radiation-curable epoxy-based compositions is reported to be cationic polymerization.
Well-known examples of radiation-curable, acrylate-based resins include those having structural backbones of urethanes, amides, imides, ethers, hydrocarbons, esters and siloxanes. [See e.g., J. G. Woods, xe2x80x9cRadiation-Curable Adhesivesxe2x80x9d in Radiation Curing: Science and Technology, 333-98, 371, S. P. Pappas, ed., Plenum Press, New York (1992).] The common cure mechanism for such radiation-curable, acrylate-based compositions is free-radical polymerization.
European Patent Publication EP 393 407 describes a radiation-curable composition which includes a slow cure cationic polymerizable epoxide, a fast cure free radical polymerizable acrylic component and a photoinitiator. Upon exposure to radiation, the photoinitiator is said to be capable of generating a cationic species which is capable of initiating polymerization of the epoxide and a free radical species which is capable of initiating polymerization of the acrylic component. The polymerizable acrylic component includes monofunctional acrylates and acrylate esters, such as cyano-functionalized acrylates and acrylate esters, examples of which are expressed as 2-cyanoethyl acrylate (CH2xe2x95x90CHCOOCH2CH2CN) and 3-cyanopropyl acrylate (CH2xe2x95x90CHCOOCH2CH2CH2CN). (See page 5, lines 19-26.) The photoinitiator includes onium salts of Group Va, VIa and VIIa as well as iron-arene complexes, and generally metallocene salts, provided that the material chosen as the photoinitiator is said to be one which is capable of generating both a cationic species and a free radical species upon exposure to radiation. (See page 5, line 56-page 7, line 15.)
Other reported information regarding photopolymerizable compositions includes formulations containing epoxy compounds and metal complexes, such as disclosed in U.S. Pat. No. 5,525,698 (Bxc3x6ttcher).
U.S. Pat. No. 4,707,432 (Gatechair) speaks to a free radical polymerizable composition which includes (a) polymerizable partial esters of epoxy resins and acrylic and/or methacrylic, and partial esters of polyols and acrylic acid and/or methacrylic acid, and (b) a photoinitiator blend of a cyclopentadienyl iron complex and a sensitizer or photoinitiator, such as an acetophenone.
In D. B. Yang and C. Kutal, xe2x80x9cInorganic and organometallic Photoinitiatorsxe2x80x9d in Radiation Curing. Science and Technology, 21-55, S. P. Pappas, ed., Plenum Press, New York (1992), cyclopentadienyl transition metal complexes are discussed with attention paid to ferrocene and titanocene. In the absence of halogenated media, Yang and Kutal report that ferrocene is photoinert, though in the presence of such media and a vinyllic source free radical initiated polymerization may occur.
And in C. Kutal, P. A. Grutsch and D. B. Yang, xe2x80x9cA Novel Strategy for Photoinitiated Anionic Polymerizationxe2x80x9d, Macromolecules, 24, 6872-73 (1991), the authors note that xe2x80x9c[c]onspicuously absent from the current catalogue of photoinitiators are those that undergo photochemical release of an anionic initiating species.xe2x80x9d The authors also note that ethyl cyanoacrylate is xe2x80x9cunaffected by prolonged (24-h) irradiation with light of wavelength  greater than 350 nmxe2x80x9d whereas in the presence of NCS+, cyanoacrylate is observed to solidify immediately, generating heat in the process. Though the NCSxe2x88x92 was not in that case generated as a result of irradiation, it was generated from the Reineckate anion upon ligand field excitation thereof with near-ultraviolet/visible light.
While metallocenes (such as ferrocenes) have been employed in acrylate-based anaerobic adhesive compositions [see e.g., U.S. Pat. No. 3,855,040 (Malofsky), U.S. Pat. No. 4,525,232 (Rooney), U.S. Pat. No. 4,533,446 (Conway) and EP ""407], it is not believed that to date a cyanoacrylate-based adhesive composition has been developed including therein a metallocene as defined herein, particularly with respect to curing through a photoinitiated mechanism.
Accordingly, a photocurable composition including a cyanoacrylate component, a metallocene component and a photoinitiator component would be desirable as possessing the benefits and advantages of cyanoacrylate-containing compositions while curing through at least a photo-induced polymerization mechanism.
The present invention meets the desire expressed above by providing compositions which include a cyanoacrylate component or a cyanoacrylate-containing formulation, a metallocene component and a photoinitiator. Desirably, such compositions are curable after exposure to radiation in the electromagnetic spectrum. Accordingly, in such radiation or photocurable compositions a polymerizingly effective amount of a photoinitiator should be used.
The photocurable compositions of this invention retain those benefits and advantages of traditional cyanoacrylate-containing compositions while curing through at least a photo-induced polymerization mechanism, thereby providing to the compositions (and cured reaction products formed therefrom) the benefits and advantages of curing through such a mechanism. More specifically, photocurable compositions according to this invention cure rapidly, and in so doing minimize the opportunity for undesirable blooming or crazing formation in the cured reaction product.
In another aspect of the present invention, there is provided a method of polymerizing a photocurable composition by providing an amount of the composition to a desired surface and exposing the composition to radiation in an amount sufficient to effect cure thereof.
In yet another aspect of the present invention, there is provided the cured reaction product formed from a photocurable composition after exposure thereof to a curingly effective amount of radiation.
The present invention will be more readily appreciated by those persons of skill in the art based on a reading of the detailed description of the invention which follows and the examples presented thereafter for illustrative purposes.
This invention relates to photocurable compositions which include a cyanoacrylate component or a cyanoacrylate-containing formulation, a metallocene component and a polymerizingly effective amount of a photoinitiator.
The cyanoacrylate component or cyanoacrylate-containing formulation includes cyanoacrylate monomers which may be chosen with a raft of substituents, such as those represented by H2Cxe2x95x90C(CN)xe2x80x94COOR, where R is selected from C1-5, alkyl, alkoxyalkyl, cycloalkyl, alkenyl, aralkyl, aryl, allyl and haloalkyl groups. Desirably, the cyanoacrylate monomer is selected from methyl cyanoacrylate, ethyl-2-cyanoacrylate, propyl cyanoacrylates, butyl cyanoacrylates, octyl cyanoacrylates, allyl-2-cyanoacrylate, xcex2-methoxyethyl-2-cyanoacrylate and combinations thereof. A particularly desirable cyanoacrylate monomer for use herein is ethyl-2-cyanoacrylate.
A variety of organometallic materials are also suitable for use herein. Those materials of particular interest herein may be represented by metallocenes within structure I: 
where
R1 and R2 may be the same or different and may occur at least once and up to as many as four times on each ring in the event of a five-membered ring and up to as many as five times on each ring in the event of a six-membered ring;
R1 and R2 may be selected from H; any straight- or branched-chain alkyl constituent having from 1 to about 8 carbon atoms, such as CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, C(CH3)3 or the like; acetyl; vinyl; allyl; hydroxyl; carboxyl; xe2x80x94(CH2)nxe2x80x94OH, where n may be an integer in the range of 1 to about 8; xe2x80x94(CH2)nxe2x80x94COOR3, where n may be an integer in the range of 1 to about 8 and R3 may be any straight- or branched-chain alkyl constituent having from 1 to about 8 carbon atoms; H; Li; Na; or xe2x80x94(CH2)nxe2x80x2, where nxe2x80x2 may be an integer in the range of 2 to about 8; xe2x80x94(CH2)nxe2x80x94OR4, wherein n may be an integer in the range of 1 to about 8 and R4 may be any straight- or branched-chain alkyl constituent having from 1 to about 8 carbon atoms; or xe2x80x94(CH2)nxe2x80x94Nxe2x80x2(CH3)3 Xxe2x88x92, where n may be an integer in the range of 1 to about 8 and X may be Clxe2x88x92, Brxe2x88x92, Ixe2x88x92, ClO4xe2x88x92 or BF4xe2x88x92;
Y1 and Y2 may not be present at all, but when at least one is present they may be the same or different and may be selected from H, Clxe2x88x92, Brxe2x88x92, Ixe2x88x92, cyano, methoxy, acetyl, hydroxy, nitro, trialkylamines, triaryamines, trialkylphospines, triphenylamine, tosyl and the like;
A and Axe2x80x2 may be the same or different and may be C or N;
m and mxe2x80x2 may be the same or different and may be 1 or 2; and
Me is Fe, Ti, Ru, Co, Ni, Cr, Cu, Mn, Pd, Ag, Rh, Pt, Zr, Hf, Nb, V, Mo and the like.
Of course, depending on valence state, the element represented by Me may have additional ligandsxe2x80x94Y1 and Y2xe2x80x94associated therewith beyond the carbocyclic ligands depicted above (such as where Me is Ti and Y1 and Y2 are Clxe2x88x92).
Alternatively, metallocene structure I may be modified to include materials such as: 
where R1, R2, Y1, Y2, A, Axe2x80x2, m, mxe2x80x2 and Me are as defined above. A particularly desirable example of such a material is where R1 and R2 are each H; Y1 and Y2 are each Cl; A and Axe2x80x2 are each N; m and mxe2x80x2 are each 2 and Me is Ru.
Within metallocene structure I, well-suited metallocene materials may be chosen from within metallocene structure II: 
where R1, R2 and Me are as defined above.
Particularly well-suited metallocene materials from within structure I may be chosen where R1, R2, Y1, Y2, m and mxe2x80x2 are as defined above, and Me is chosen from Ti, Cr, Cu, Mn, Ag, Zr, Hf, Nb, V and Mo.
Desirably, the metallocene is selected from ferrocenes (i.e., where Me is Fe), such as ferrocene, vinyl ferrocenes, ferrocene derivatives, such as butyl ferrocenes or diarylphosphino metal-complexed ferrocenes [e.g., 1,1-bis(diphenylphosphino) ferrocene-palladium dichloride], titanocenes (i.e., where Me is Ti), such as bis(xcex75-2,4-cyclopentadien-1-yl)-bis-[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl] titanium which is available commercially from Ciba-Geigy Corporation, Tarrytown, N.Y. under the tradename xe2x80x9cIRGACURExe2x80x9d 784DC, and derivatives and combinations thereof. A particularly desirable metallocene is ferrocene.
And bis-alkylmetallocenes, for instance, bis-alkylferrocenes (such as diferrocenyl ethane, propanes, butanes and the like) are also desirable for use herein, particularly since about half of the equivalent weight of the material (as compared to a non-bis-metallocene) may be employed to obtain the sought-after results, all else being unchanged. Of these materials, diferrocenyl ethane is particularly desirable.
Of course, other materials may be well-suited for use as the metallocene component. For instance, Me[CW3xe2x80x94COxe2x80x94CHxe2x95x90C(Oxe2x88x92)xe2x80x94CWxe2x80x23]2, where Me is as defined above, and W and Wxe2x80x2 may be the same or different and may be selected from H, and halogens, such as F and Cl. Examples of such materials include platinum (II) acetyl acetonate (xe2x80x9cPtACACxe2x80x9d), cobalt (II) acetyl acetonate (xe2x80x9cCoACACxe2x80x9d), nickel (II) acetyl acetonate (xe2x80x9cNiACACxe2x80x9d) and copper (II) acetyl acetonate (xe2x80x9cCuACACxe2x80x9d). Combinations of those materials may also be employed.
A number of photoinitiators may be employed herein to provide the benefits and advantages of the present invention to which reference is made above. Photoinitiators enhance the rapidity of the curing process when the photocurable compositions as a whole are exposed to electromagnetic radiation. Certain metallocenes, such as xe2x80x9cIRGACURExe2x80x9d 784DC, may serve a dual purpose as both metallocene and photoinitiator.
Examples of suitable photointiators for use herein include, but are not limited to, photoinitiators available commercially from Ciba-Geigy Corp., Tarrytown, N.Y. under the xe2x80x9cIRGACURExe2x80x9d and xe2x80x9cDAROCURxe2x80x9d tradenames, specifically xe2x80x9cIRGACURExe2x80x9d 184 (1-hydroxycyclohexyl phenyl ketone), 907 (2-methyl-1-[4-(methylthio)phenyl]-2-morpholino propan-1-one), 369 (2-benzyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)-1-butanone), 500 (the combination of 1-hydroxy cyclohexyl phenyl ketone and benzophenone), 651 (2,2-dimethoxy-2-phenyl acetophenone), 1700 (the combination of bis(2,6-dimethoxybenzoyl-2,4,4-trimethyl pentyl)phosphine oxide and 2-hydroxy-2-methyl-1-phenyl-propan-1-one), and 819 [bis(2,4,6-trimethyl benzoyl)phenyl phosphine oxide] and xe2x80x9cDAROCURxe2x80x9d 1173 (2-hydroxy-2-methyl-1-phenyl-1-propane) and 4265 (the combination of 2,4,6-trimethylbenzoyldiphenyl-phosphine oxide and 2-hydroxy-2-methyl-1-phenyl-propan-1-one); and the visible light [blue] photoinitiators, dl-camphorquinone and xe2x80x9cIRGACURExe2x80x9d 784DC. Of course, combinations of these materials may also be employed herein.
Other photoinitiators useful herein include alkyl pyruvates, such as methyl, ethyl, propyl, and butyl pyruvates, and aryl pyruvates, such as phenyl, benzyl, and appropriately substituted derivatives thereof.
Photoinitiators particularly well-suited for use herein include ultraviolet photoinitiators, such as 2,2-dimethoxy-2-phenyl acetophenone (e.g., xe2x80x9cIRGACURExe2x80x9d 651), and 2-hydroxy-2-methyl-1-phenyl-1-propane (e.g., xe2x80x9cDAROCURxe2x80x9d 1173), bis(2,4,6-trimethyl benzoyl)phenyl phosphine oxide (e.g., xe2x80x9cIRGACURExe2x80x9d 819), and the ultraviolet/visible photoinitiator combination of bis(2,6-dimethoxybenzoyl-2,4-,4-trimethylpentyl)phosphine oxide and 2-hydroxy-2-methyl-1-phenyl-propan-1-one (e.g., xe2x80x9cIRGACURExe2x80x9d 1700), as well as the visible photoinitiator bis(xcex7s-2,4-cyclopentadien-1-yl)-bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl]titanium (e.g., xe2x80x9cIRGACURExe2x80x9d 784DC).
With respect to formulating photocurable compositions, generally the components may be introduced to one another in any convenient order. Alternatively, it may be desirable to prepare a premix of the metallocene component and the photoinitiator component. In this way, a ready made premix of those components may be added to the cyanoacrylate component of the formulation to allow for a quick and easy one-part formulation of a photocurable composition prior to dispensing and curing thereof.
For packaging and dispensing purposes, it may be desirable for photocurable compositions in accordance with the present invention to be relatively fluid and flowable. Variations in the viscosity thereof may also be desirable in certain applications and may be readily achieved through routine changes in formulation, the precise changes being left to those persons of ordinary skill in the art.
For instance, ordinarily cyanoacrylate-containing compositions free from an added thickener or viscosity modifier are low viscosity formulations (such as in the range of 1 to 3 cps). While a composition with such a is viscosity (or one whose viscosity has been modified to be up to about five times that viscosity) may be appropriate for a wicking application where a small gap exists between substrates to be bound (e.g., less than about 0.1 mils) and/or an application where enhanced cure speed is desirable, such a viscosity may be too low for convenient use in certain industrial applications. At least for this reason, the viscosity of cyanoacrylate-containing compositions has at times been desirably modified through, for instance, the addition of polymethylmethacrylates and/or fumed silicas. See e.g., U.S. Pat. No. 4,533,422 (Litke) and Re. 32,889 (Litke), the disclosures of each of which are hereby expressly incorporated herein by reference.
A medium viscosity formulation (such as in the range of 100 to 300 cps) may be more appropriate in applications where greater control of flowability is desirable such as bonding together molded polymeric parts. And a high viscosity formulation (such as in the range of 600 to 1000 cps) may be more appropriate in applications involving porous substrates and/or substrates with larger gaps (such as greater than about 0.5 mils).
Of course, those of ordinary skill in the art should make appropriate decisions regarding whether a viscosity modifier should be included in the photocurable composition, and if so which one(s) and at what level should one be included to achieve the desired viscosity for the intended applications.
In addition, it may be desirable to toughen the cured photocurable compositions of the present invention through the addition of elastomeric rubbers such as is taught by and claimed in U.S. Pat. No. 4,440,910 (O""Connor), the disclosure of which is hereby expressly incorporated herein by reference. It may also be desirable to improve the hot strength of the cured photocurable compositions by addition of anhydrides, such as is taught by and claimed in U.S. Pat. No. 4,450,265 (Harris) and the documents cited therein, the disclosures of each of which are hereby expressly incorporated herein by reference.
Moreover, the compositions of the present invention may be rendered into a thixotropic paste through addition of powdered organic fillers having a particle size of about 2 to 200 microns as is taught by U.S. Pat. No. 4,105,715 (Gleave) or thickened by a copolymer or terpolymer resin to improve peel strength as is taught by U.S. Pat. No. 4,102,945 (Gleave), the disclosures of each of which are hereby incorporated herein by reference.
Further, the compositions of the present invention may be rendered more resistant to thermal degradation at elevated temperature conditions by the inclusion of certain sulfur-containing compounds, such as sulfonates, sulfinates, sulfates and sulfites as set forth in U.S. Pat. No. 5,328,944 (Attarwala), the disclosure of which is hereby expressly incorporated herein by reference. The inclusion of such compounds in the photocurable compositions of the present invention renders those compositions well-suited for applications in which elevated temperature conditions may be experienced, such as with potting compounds particularly where large cure through volume is present and non-tacky surfaces are desirably formed in less than about five seconds.
The sulfur-containing compounds effective for enhancing the thermal resistance of the cured cyanoacrylate polymer may be represented according to the formula: 
where R1 and R2 are, respectively, monovalent and divalent hydrocarbon groups which may be optionally substituted with halogen, NO2, oxo (xe2x95x90O), CN, alkoxy, hydroxy, acyloxy or SO2 or interrupted by one or more ether oxygen atoms.
The sulfur-containing compounds are suitably employed at levels of about 0.1-10% by weight of the inventive composition.
More specifically, the thermal resistance conferring compound used in the inventive compositions, include by way of example, acyclic and cyclic sulfates, such as diphenyl sulfate, dibutyl sulfate; and compounds, such as 1,3,2-dioxathiolene-4-ethyl-2,2-dioxide and the di(cyclic sulfate) of 1,2,7,8-octane tetraol which have one or more groups of the formula: 
where R3 is independently H, alkyl or aryl; anhydrosulfites, such as xcex1-hydroxyisobutynic acid anhydrosulfite; sulfoxides such as dibutylsulfoxide, di-xcex1,xcex1xe2x80x2-phenylethylsulfoxide and xcex1-methylthioxo-butyrolactone; sulfites such as glycol sulfite, dimethyl sulfite diethyl sulfite and o-phenylene sulfite; sulfonates, such as ethyl methanesulfonate, ethyl trifluoromethane sulfonate, methyl p-toluenesulfonate, n-butyl p-toluenesulfonate, benzyl p-toluenesulfonate, xcex1-methylbenzyl p-toluenesulfonate, xcex1,xcex1-dimethylbenzyl p-toluenesulfonate and the diethyl ester of acetone disulfonic acid; and sulfinates such as methyl-p-toluenesulfonate.
These compounds are usefully employed at levels in the range of about 0.1%-10% by weight of the inventive composition, preferably at least 0.5% and more typically about 0.75%-5% by weight of the inventive composition.
The inclusion of such materials to a photocurable composition in accordance with the present invention may provide a formulation having particular advantages for certain applications, and at least in the case of viscosity modifiers should be appealing from a safety perspective as the possibility is decreased of splashing or spilling the composition on exposed skin of the user or bystanders. In addition, since the parts to be bonded with the inventive compositions are fixed by exposure to UV radiation, there is less of a chance for the assembler to touch or contact an uncured fillet.
The relative amount of the various components of the photocurable compositions according to this invention is a matter of choice left to those persons of skill in the art, depending of course on the identity of the particular components chosen for a specific composition. As a general guide, however, it is desirable to include in the photocurable compositions a metallocene, such as ferrocene, in an amount within the range of about 0.005% to about 4% or greater (desirably within the range of about 0.01% to about 1.5%) by weight of the total composition. It is also desirable for the compositions to include a photoinitiator, such as xe2x80x9cIRGACURExe2x80x9d 1700 or 819, or xe2x80x9cDAROCURxe2x80x9d 1173, in an amount within the range of about 0.125% to about 10% by weight of the composition, with about 2% to about 4% or greater by weight of the total composition being desirable. The balance of the composition is composed predominantly of a cyanoacrylate component, such as ethyl-2-cyanoacrylate. Of course, the amount of all the components together in the composition totals 100%.
A method of curing a photocurable composition in accordance with this invention is also provided herein, the steps of which include (a) providing onto a desired substrate an amount of a photocurable composition; and (b) subjecting the composition to radiation sufficient to effect cure thereof.
The amount of photocurable composition provided should be sufficient to cure and form an adequate bond to the substrate surfaces between which it is applied. For instance, application of the photocurable composition may he achieved by dispensing the composition in drop-wise fashion, or as a liquid stream, brush-applied, dipping, and the like, to form a thin film. Application of the photocurable composition may depend on the flowability or viscosity of the composition. To that end, viscosity modifiers, as noted above, may be included in the composition.
In use, such compositions are desirably readily dispensed onto a portion of a desired surface of a substrate onto which is to be bonded a portion of another substrate. The photocurable composition may be applied to certain portions of the substrate surface or over the entire surface of the substrate to be bonded, depending on the particular application.
The source of radiation emitting electromagnetic waves is selected from ultraviolet light, visible light, electron beam, x-rays, infrared radiation and combinations thereof. Desirably, ultraviolet light is the radiation of choice, with appropriate sources including xe2x80x9cHxe2x80x9d, xe2x80x9cDxe2x80x9d, xe2x80x9cVxe2x80x9d, xe2x80x9cXxe2x80x9d, xe2x80x9cMxe2x80x9d and xe2x80x9cAxe2x80x9d lamps, mercury arc lamps, and xenon arc lamps (such as those commercially available from Loctite Corporation, Rocky Hill, Conn., Fusion UV Curing Systems, Buffalo Grove, Ill. or Spectroline, Westbury, N.Y.); microwave-generated ultraviolet radiation; solar power and fluorescent light sources. Any of these electromagnetic radiation sources may use in conjunction therewith reflectors and/or filters, so as to focus the emitted radiation onto a specific portion of a substrate onto which has been dispensed a photocurable composition and/or within a particular region of the electromagnetic spectrum. Similarly, the electromagnetic radiation may be generated directly in a steady fashion or in an intermittent fashion so as to minimize the degree of heat build-up. Although the electromagnetic radiation employed to cure the photocurable compositions into desired reaction products is often referred to herein as being in the ultraviolet region, that is not to say that other radiation within the electromagnetic spectrum may not also be suitable. For instance, in certain situations, radiation in the visible region of the electromagnetic spectrum may also be advantageously employed, whether alone or in combination with, for instance, radiation in the ultraviolet region. Of course, microwave and infrared radiation may also be advantageously employed under appropriate conditions.
Higher or lower radiation intensities, greater or fewer exposures thereto and length of exposure and/or greater or lesser distances of the source of radiation to the composition may be required to complete curing, depending of course on the particular components of a chosen composition.
More specifically with respect to radiation intensity, the chosen lamp should have a power rating of at least about 100 watts per inch (about 40 watts per cm), with a power rating of at least about 300 watts per inch (about 120 watts per cm) being particularly desirable. Also, since the inclusion of a photoinitiator in the composition may shift the wavelength within the electromagnetic radiation spectrum at which cure occurs, it may be desirable to use a source of electromagnetic radiation whose variables (e.g., wavelength, distance, and the like) are readily adjustable.
During the curing process, the composition will be exposed to a source of electromagnetic radiation that emits an amount of energy, measured in KJ/m2, determined by parameters including: the size, type and geometry of the source; the duration of the exposure to electromagnetic radiation; the intensity of the radiation (and that portion of radiation emitted within the region appropriate to effect curing); the absorbency of electromagnetic radiation by any intervening materials, such as substrates; and the distance the composition lies from the source of radiation. Those persons of skill in the art should readily appreciate that curing of the composition may be optimized by choosing appropriate values for these parameters in view of the particular components of the composition.
To effect cure, the source of electromagnetic radiation may remain stationary while the composition passes through its path. Alternatively, a substrate coated with the photocurable composition may remain stationary while the source of electromagnetic radiation passes thereover or therearound to complete the transformation from composition to reaction product. Still alternatively, both may traverse one another, or for that matter remain stationary, provided that the photocurable composition is exposed to electromagnetic radiation sufficient to effect cure.
Commercially available curing systems, such as the xe2x80x9cZETAxe2x80x9d 7200 or 7400 ultraviolet curing chamber (Loctite Corporation, Rocky Hill, Conn.), Fusion UV Curing Systems F-300 B (Fusion UV Curing Systems, Buffalo Grove, Ill.), Hanovia UV Curing System (Hanovia Corp., Newark, N.J.), BlackLight Model B-100 (Spectroline, Westbury, N.Y.) and RC500 A Pulsed UV Curing System (Xenon Corp., Woburn, Mass.), are well-suited for the purposes described herein. Also, a Sunlighter UV chamber fitted with low intensity mercury vapor lamps and a turntable may be employed herein.
The required amount of energy may be delivered by exposing the composition to a less powerful source of electromagnetic radiation for a longer period of time, through for example multiple passes, or alternatively, by exposing the composition to a more powerful source of electromagnetic radiation for a shorter period of time. In addition, each of those multiple passes may occur with a source at different energy intensities. In any event, those persons of skill in the art should choose an appropriate source of electromagnetic radiation depending on the particular composition, and position that source at a suitable distance therefrom which, together with the length of exposure, optimizes transformation. Also, it may be desirable to use a source of electromagnetic radiation that is delivered in an intermittent fashion, such as by pulsing or strobing, so as to ensure a thorough and complete cure without causing excessive heat build-up.
In use, a photocurable composition in accordance with the present invention may be dispensed, such as in the form of a thin film or droplet, onto a desired substrate. Substrates onto which the photocurable composition of the present invention may be applied may be chosen from a vast selection of different materials; basically, any material with which cyanoacrylates may be used is suitable as well for use herein. See supra.
Desirable choices among such materials include acrylics, epoxies, polyolefins, polycarbonates, polysulfones (e.g., polyether sulfone), polyvinyl acetates, polyamides, polyetherimides, polyimides and derivatives and co-polymers thereof with which may be blended or compounded traditional additives for aiding processibility or modifying the physical properties and characteristics of the material to be used as a substrate. Examples of co-polymers which may be employed as substrates include acrylonitrile-butadiene-styrene, styrene-acrylonitrile cellulose, aromatic copolyesters based on terephthallic acid, p,p-dihydroxybiphenyl and p-hydroxy benzoic acid, polyalkylene (such as polybutylene or polyethylene)terephthalate, polymethyl pentene, polyphenylene oxide or sulfide, polystyrene, polyurethane, polyvinylchloride, and the like. Particularly, desirable co-polymers include those which are capable of transmitting UV and/or visible radiation. Of course, other materials may also be employed as substrates, such as metals, like stainless steel.
The composition-coated substrate may be positioned within an electromagnetic radiation curing apparatus, such as the xe2x80x9cZETAxe2x80x9d 7200 ultraviolet curing chamber, equipped with an appropriate source of electromagnetic radiation, such as ultraviolet radiation, at an appropriate distance therefrom, such as within the range of about 1 to 2 inches (2.54 to 5.08 cm), with about 3 inches (7.62 cm) being desirable. As noted above, the composition-coated substrate may remain in position or may be passed thereunder at an appropriate rate, such as within the range of about 1 to about 60 seconds per foot, with about 5 seconds per foot being desirable. Such passage may occur one or more times, or as needed to effect cure of the composition on the substrate. The length of exposure may be in the range of a few seconds or less (for one time exposure) to tens of seconds or longer (for either a one time exposure or a multiple pass exposure) if desired, depending on the depth of the composition to be cured and of course on the components of the composition themselves.
A reaction product is also of course provided by the teaching of this invention. The reaction product is formed from photocurable compositions after exposure thereof to electromagnetic radiation sufficient to effect cure of the composition. The reaction product is formed rapidly, and ordinarily and desirably without observed formation of blooming or crazing, see infra.
The reaction product of the photocurable composition may be prepared by dispensing in low viscosity or liquid form a photocurable composition in accordance with the present invention onto a substrate and mating that substrate with a second substrate to form an assembly. Thereafter, exposure to electromagnetic radiation on at least one substrate of the assembly for an appropriate period of time should transform the photocurable composition into an adhesive reaction product.
It is also within the scope of the present invention for reaction products to be prepared from a photocurable composition separately from the device, and thereafter positioned on a substrate surface with which it is to be used. In this manner, such reaction products may desirably be fabricated, for instance, into a film or tape, such as an adhesive film or a coating film, which when applied to a chosen substrate will bond thereto. Many known film manufacturing processes may be employed to manufacture into films photocurable compositions in accordance with the present invention, including calendaring, casting, rolling, dispensing, coating, extrusion and thermoforming. For a non-exhaustive description of such processes, see Modern Plastics Encyclopedia 1988, 203-300, McGraw-Hill Inc., New York (1988). With respect to dispensing or coating, conventional techniques, such as curtain coating, spray coating, dip coating, spin coating, roller coating, brush coating or transfer coating, may be used.
A film of the photocurable composition may be prepared by extrusion or calendaring, where cure occurs by exposure to electromagnetic radiation prior to, contemporaneously with, or, if the composition is sufficiently viscous, after passing through the extruder or calendar. Thereafter, the film may be placed between the desired substrates, and construction of the device may be completed.
The viscosity of the photocurable composition may be controlled or modified to optimize its dispensability by, in addition to inclusion of an appropriate material to alter the viscosity thereof as noted above, adjusting the temperature of (1) the composition itself, or (2) the substrates on which the composition may be placed to assemble the device. For example, the temperature of the composition or the substrate(s) or combinations thereof may be decreased to increase the viscosity of the composition. In this way, the uniformity on the substrate of the dispensed photocurable composition may be enhanced using lamination techniques, centrifuge techniques, pressure applied from the atmosphere (such as with vacuum bagging), pressure applied from a weighted object, rollers and the like.
The substrates onto which the photocurable compositions of the present invention are intended to be dispensed may be constructed from the litany of materials recited supra, which may be substantially inflexible as well as flexible. The type of substrate chosen with respect to flexibility will of course depend on the application for which it is to be used. More specifically, the substrates may be constructed from substantially inflexible materials, such as glass, laminated glass, tempered glass, optical plastics, such as polycarbonates, acrylics and polystyrenes, and other alternatives as noted supra; and flexible materials, such as xe2x80x9cMYLARxe2x80x9d film or polyolefin, such as polyethylene or polypropylene, tubing.
The choice of substrate material may influence the choice of processing technique used to prepare the photocurable composition into the cured reaction product or the type of device assembled. For example, when assembling a device from at least one flexible substrate, a composition may be advantageously applied to an end portion of the flexible substrate and allowed to wick along that end portion through a portion of another substrate, which is dimensioned to receive that end portion of the flexible substrate. A particular example of such an application is polyolefin tubing intended for medical application, one end portion of which is dimensioned for receiving by an acrylic luer housing.
In addition, roll-to-roll systems may be employed where flexible substrates are released from rolls (that are aligned and rotate in directions opposite to one another), and brought toward one another in a spaced-apart relationship. In this way, the photocurable composition may be dispensed or injected onto one of the flexible substrates at a point where the two flexible substrates are released from their respective rolls and brought toward one another, while being contemporaneously exposed to electromagnetic radiation for a time sufficient to cure the composition into an adhesive reaction product.
The dispensing of the composition may be effected through an injection nozzle positioned over one of the rolls of flexible substrate. By passing in the path of the nozzle as a continuously moving ribbon, a flexible substrate may be contacted with the composition in an appropriate amount and positioned on the flexible substrate.
Since the photocurable compositions of the present invention cure to form reaction products through, as their description connotes, a photo-initiated mechanism, the composition and the surface of the substrate on which the composition is placed should be exposed to the source of electromagnetic radiation. The choice of substrate may affect the rate and degree at which cure occurs of the photocurable compositions of the present invention. For instance, it is desirable for the substrates to be bonded together to be substantially free of electromagnetic radiation-absorbing capabilities. That is, the greater degree of electromagnetic radiation transmitting capability the substrate possesses, the greater the rate and degree of cure of the composition, all else being equal of course.
Blooming or crazing may be observed when compositions cure into reaction products and the cure itself is incomplete. That is, blooming refers to the evaporation of cyanoacrylate monomer (due to its relatively high vapor pressure) from uncured fillets, the result of which is formation of a precipitate on surfaces adjacent to the bond line which are also observed as a white haze. Crazing refers to the formation of stress cracks on certain synthetic materials, such as polycarbonates, acrylics and polysulfones, due in this instance to the presence thereon of cyanoacrylate monomer.
The result of incomplete curing may be observed with respect to adhesive uses of the photocurable composition as adhesive or cohesive failure of the cured composition when applied to or between substrates. Such observations may be minimized or even eliminated by using electromagnetic radiation transmitting (as contrasted to absorbing) substrates and placing the source of electromagnetic radiation at a strategic location so as to improve the degree of electromagnetic radiation to which the composition on the substrate is exposed. Similarly, additional sources of electromagnetic radiation, or as stated above reflectors which redirect onto desired portions of the substrate stray or errant electromagnetic radiation, may be employed to further enhance cure.
Accordingly, the compositions of this invention provide a number of benefits and advantages. These include: a built-in secondary cure system (i.e., photo-initiation in addition to the ordinary cyanoacrylate anionic initiation), which is particularly attractive in those applications where certain of the substrates which may be used in the assembly do not allow the transmission of light, rendering another type of adhesive (such as a dual cure acrylic adhesive) less desirable because a secondary heating step would then be required; elimination of a substrate primer step, which obviates the use of often flammable materials and invites automated processes; and improves the cure though gap.
In view of the above description of the present invention, it is evident that a wide range of practical opportunities is provided by the teaching herein. Certain of those practical opportunities are exemplified below, as are many of the advantages and benefits of the present invention. However, the invention as so exemplified is for illustrative purposes only and is not to be construed in any way as limiting the broad aspects of the teaching herein provided.